Sand-lightweight Concrete Research Articles

Effects of aggregate types and softening effect on multiaxial mechanical properties of lightweight aggregate concrete

Softening effect refers to the inherent property of porous media materials of having their strength decrease over time under water saturation compared with that under dry condition. Typical porous media materials, such as ceramsite and ceramsite-based concrete, exhibit a softening effect. This study investigated the softening effect of shale ceramsite (SC) and different types of lightweight aggregate concrete (LWACs). Mix ratios of LC30 all-lightweight shale ceramsite concrete (also known as all-lightweight concrete, ALWC) whose SC and shale pottery (SP) were selectively or simultaneously replaced with limestone gravel (LSG) and river sand (RS) with the same volume fraction, respectively, were prepared for comparison with gravel lightweight concrete (GLWC), sand lightweight concrete (SLWC) and hybrid aggregate lightweight concrete (HALWC) were formed. The four kinds of LWACs (ALWC, GLWC, SLWC and HALWC) were cast into their corresponding specification and size specimens and demoulded after indoor curing for 24 h, with their target ages (7–180 d) maintained under standard and hydrostatic curing. Then, the strength and initial elastic modulus under uniaxial stress, ultimate compressive strength and stress–strain curves under triaxial stress of the specimens were tested to analyse the influence of aggregate types and curing methods on the mechanical properties and softening effect of LWACs. According to the test results, the cube compression, prism compression, splitting tensile, conventional triaxial compression and elastic modulus decreased after 180 d of hydrostatic curing; the experimental age of the conventional triaxial compression test was after 90 d. ALWC demonstrated the most evident decrease, followed by SLWC, HALWC and GLWC. The trend indicates that normal aggregates can significantly improve the softening effect of LWACs. The failure modes of the triaxial compression specimens changed from splitting failure to shear failure, and a plastic platform phenomenon was apparent on the stress–strain curves, with their descending section appearing gentler than those in the uniaxial compression test with the increase in confining pressure. The relationship between ultimate compressive strength and confining pressure of the LWACs can be accurately described by the Mohr–Coulomb single-parameter failure criterion, Hsieh–Ting–Chen four-parameter failure criterion and Willam–Warnke five-parameter failure criterion. However, the three failure criteria demonstrated application limitations based on meridian equation and deviatoric plane analysis. The extension trend of the compression meridian of the LWACs after 90 d of hydrostatic curing was generally the same, and the types of aggregates exerted a minimal effect on the meridian and deviatoric plane limit trace. The softening effect of LWACs was mainly caused by the softening effect of the SC itself and the influence of pore water on the matrix concrete.

Pull-off bond strength of novel wide rounded ends fiber and impact of fiber stretching on fiber/matrix frictional-slip bond strength

ABSTRACT This paper presents a study about fiber slippage behavior under direct pull-out and assessment of fiber/matrix pull-off bond strength. This study was prepared through theoretical calculations validated by experimental tests. Theoretically, the study shows a general solution for the fiber-slip mechanism in a general matrix using a new frictional-shear-lag model and an analytical model for pull-off bond strength. Experimentally, pull-out tests were conducted for selected types of single fiber in micro-level (glass, carbon, and short-steel fiber); and macro-level (straight steel fiber). The results showed significant improvements in the pull-off bond strength using novel shape of fiber with wide rounded ends-WESF. The pull-off bond strength in normal-weight concrete was found lower than in lightweight concrete, and the matrix with higher compressive strength improves the pull-off bond strength. Also, the steel fiber showed higher pull-off bond strength compared to glass and carbon fiber; whereas the efficiency of short-steel fiber was higher than the long one. All types of fiber showed that the higher aspect ratio reduces the pull-off bond strength. Using the novel-WESF, the performance of fiber-slip improved 52.65% in normal-weight concrete. Moreover, the fiber-slip performance improved 61.79% in sand-lightweight concrete, and 70.20% in all other types of light-weight concrete.

Flexural behaviour of lightweight aggregate concrete columns

The flexural performance of lightweight concrete (LWC) columns was evaluated and limitations of ACI 318-19 in predicting the flexural crack (Mcr) and maximum (Mn) moments, as well as the minimum amount of transverse reinforcing bar (Ash(ACI)), were examined. Six LWC columns with different amounts of transverse reinforcing bar (Ash), compressive strengths of concrete (fc′) and concrete types were prepared and tested under constant axial and cyclic lateral loads. The test results show that ACI 318-19 agrees well with the Mcrof tested columns, considering the lower tensile stress of LWC columns by introducing modification factors (λ) (all-lightweight concrete, λ = 0.75; sand–lightweight concrete, λ = 0.85) for the fracture modulus of concrete (fr). In addition, ACI 318-19 underestimates Mn, irrespective of Ash, fc′ and concrete type. The ductility of LWC columns increased with the increase in volumetric transverse reinforcing bar index (ωvh). The increasing rate was lower than that of normal-weight concrete (NWC) columns. The displacement ductility ratio (μΔ), work damage indicator (W80) and equivalent damping coefficient (ξ80) of a column with 1.0Ash(ACI)were, on average, 30, 36 and 18% lower in LWC than NWC columns. Consequently, double the Ash(ACI)was required to retain a flexural ductility equivalent to that of a NWC specimen.

Bond Performance between Normal-Strength Concrete and Sand-Lightweight Concrete

Bond Performance between Normal-Strength Concrete and Sand-Lightweight Concrete

Fabrication and properties of high-performance microporous gravel using waste materials

This work addresses the production of high-strength micro-porous aggregate from metallurgical plant glass waste. The proposed technology enables for a wider range of raw materials to be used in the production of porous aggregates for lightweight concretes.According to the findings, granulated slags from metallurgical industries, which are a by-product of process, can be used as a fundamental beginning raw material for creating an artificial porous aggregate. The expansion intervals of a mass based on acid and basic slags of metallurgical industries are estimated based on the findings of the investigations. It has been figured out how to make a high-strength porous aggregate with predefined physico-mechanical properties. The main physico-mechanical characteristics of the produced aggregate have been studied. It has been found that the obtained artificial porous aggregate meets the requirements of the acting standard GOST 9757–90 “Gravel, Crushed Stone and Sand, Artificial Porous” by its physico-mechanical characteristics. It is revealed that the strength of the obtained aggregate 1.8–2.2 times exceeds that of the well-known aggregate- keramzit gravel. With the use of porous sand lightweight concrete of class B7.5-B40 by strength with density of 1100–1600 kg/m3 has been produced on the base of the obtained gravel and by using dense sand and plasticizing additives high-strength lightweight concrete of class B25-B50 with density of 1500–1800 kg/m3 has been manufactured.

Mechanical performance of sand-lightweight concrete-filled steel tube stub column under axial compression

In order to study the axial compression performance of sand-lightweight concrete-filled steel tube (SLCFST) stub columns, three circular SLCFST (C-SLCFST) stub column specimens and three SLCFST square (S-SLCFST) stub column specimens were fabricated and static monotonic axial compression performance testing was carried out, using the volume ratio between river sand and ceramic sand in sand-lightweight concrete (SLC) as a varying parameter. The stress process and failure mode of the specimens were observed, stress-strain curves were obtained and analysed for the specimens, and the ultimate bearing capacity of SLCFST stub column specimens was calculated based on unified strength theory, limit equilibrium theory and superposition theory. The results show that the outer steel tubes of SLCFST stub columns buckled outward, core SLC was crushed, and the damage to the upper parts of the S-SLCFST stub columns was more serious than for C-SLCFST stub columns. Three stages can be identified in the stress-strain curves of SLCFST stub columns: an elastic stage, an elastic-plastic stage and a plastic stage. It is suggested that AIJ-1997, CECS 159:2004 or AIJ-1997, based on superposition theory, can be used to design the ultimate bearing capacity under axial compression for C-SLCFST and S-SLCFST stub columns; for varying replacement ratios of natural river sand, the calculated stress-strain curves for SLCFST stub columns under axial compression show good fitting to the test measure curves.

Bond Characteristic of All-Lightweight Concrete and Sand-Lightweight Concrete with Sand Coated GFRP Bar

Bond Characteristic of All-Lightweight Concrete and Sand-Lightweight Concrete with Sand Coated GFRP Bar

Risk of Thermal Cracking from Use of Lightweight Aggregate in Mass Concrete

This paper describes the results of a numerical investigation of incorporating lightweight aggregate (LWA) in mass concrete structures. Numerical simulation was performed with ConcreteWorks software on three rectangular piers for normal weight concrete, internally cured concrete, sand–lightweight concrete, and all–lightweight concrete. Results show that temperature differences greater than 35°F may not necessarily introduce thermal cracking in mass concrete made with LWA. Maximum core temperatures and temperature differences increased with decreasing concrete density; however, the cracking risk of the mass concrete elements decreased as a greater quantity of LWA was used, regardless of element size. This trend occurred because other properties, such as coefficient of thermal expansion, creep, modulus of elasticity, tensile strength, and geometrical conditions, influenced the risk of thermal cracking. Additionally, the identification of the cross-section locations involved in measuring the critical temperature difference in a mass concrete structure are presented. The results of this work can be helpful in identifying critical stress locations in cross sections and assessing the cracking risk for mass concrete structures. A temperature and stress analysis is recommended before mass concrete construction involving LWA is begun.

Tests on direct tensile characteristics of expanded clay lightweight aggregate concrete

The tensile characteristics of lightweight aggregate concrete under direct tension were examined with a view to enhancing the utilisation of artificially expanded clay granules as secondary aggregates. Ready-mixed concrete specimens were classified into two groups: all-lightweight concrete (ALWC) and sand-lightweight concrete (SLWC). The test parameters considered for each group were the maximum aggregate size (4–19 mm) and the lateral depth of specimens with a rectangular section (100–500 mm). The complete stress–crack mouth opening displacement (CMOD) response was measured under direct tension. The results show that the slope of the ascending branch of the stress–CMOD curve is slightly smaller for SLWC specimens than for ALWC specimens. The displacement at peak stress tends to increase with the lateral depth of the specimen, whereas the tensile strength of the concrete decreases, revealing the size effect phenomenon. However, the tensile strength of concrete and the softening slope at the descending branch of the stress–CMOD curve are marginally affected by the specimen's lateral depth and maximum aggregate size, owing to the reduced aggregate interlocking capacity across the crack. Gopalaratnam and Shah's model was modified to evaluate the stress–CMOD responses of the lightweight aggregate concretes, and the suggested and existing models were compared with the test results.

Seismic Investigation of Interior Reinforced Concrete Sand-Lightweight Concrete Beam-Column Joints

Seismic Investigation of Interior Reinforced Concrete Sand-Lightweight Concrete Beam-Column Joints

Interface shear transfer of lightweight-aggregate concretes cast at different times

This study examined the direct shear transfer across an in- terface of lightweight aggregate concretes cast at different times. Increasing use of lightweight aggregate concretes prompted this investigation to determine the appropri- ateness of current shear friction design provisions with respect to all-lightweight and sand-lightweight concrete. The experimental investigation included 36 push-off specimens constructed with a cold joint along the shear plane. Test variables included concrete type (unit weight), compressive strength of concrete, and surface preparation of the shear interface. A constant amount of reinforcing steel (1.33%) was provided across the shear plane. Applied shear force–slip relations were presented and discussed. Peak and residual shear strengths were also compared. Results suggest that concrete type did not play a significant role in the shear strength of the specimens in this study. Shear strengths computed using the shear friction design provisions in the Building Code Requirements for Struc- tural Concrete (ACI 318-11) and Commentary (ACI 318R- 11) and PCI Design Handbook: Precast and Prestressed Concrete were conservative for the sand-lightweight and all-lightweight specimens.

Direct tensile strength of lightweight concrete with different specimen depths and aggregate sizes

To examine the size effect in direct tension, 8 ready-mixed concrete batches classified into all-lightweight concrete (ALWC) and sand-lightweight concrete (SLWC) groups were prepared. In each group, the maximum aggregate size varied between 4mm and 19mm, and then the lateral depth of specimen with rectangular section ranged from 100mm to 500mm in each concrete batch. The size effect curves based on the basic formulas proposed by Bažant (1984) [1], Kim and Eo (1990) [2], and Yang and Sim (2011) [3] were also determined using a total of 28 lightweight concrete (LWC) data of current tests and 114 normal-weight concrete (NWC) data compiled from the available literature (Carpinteri and Ferro, 1994; Hu, 2011) [4,5], though specimens with lateral depth beside 100mm is very insufficient even in NWC. The present experimental observations and verifications by prediction models clearly showed that the size effect is more notable with the decrease of the unit weight of concrete and it is stronger in direct tension than in compression. The validity of Bažant’s model (Bažant, 1984) [1] is significantly dependent on the maximum aggregate size, while the models proposed by Kim and Eo (1990) [2] and Yang and Sim (2011) [3] closely predict the size effect trend observed from test data, confirming that the influence of the maximum aggregate size on the concrete tensile strength and the size effect is negligible, especially for LWC.

Development of lightweight concrete with high resistance to water and chloride-ion penetration

Abstract This paper presents an experimental study to evaluate the influence of coarse lightweight aggregate (LWA), fine LWA and the quality of the paste matrix on water absorption and permeability, and resistance to chloride-ion penetration in concrete. The results indicate that incorporation of pre-soaked coarse LWA in concrete increases water sorptivity and permeability slightly compared to normal weight concrete (NWC) of similar water-to-cementitious materials ratio (w/cm). Furthermore, resistance of the sand-lightweight concrete (LWC) to water permeability and chloride-ion penetration decreases with an increase in porosity of the coarse LWA. The use of fine LWA including a crushed fraction

Mixture Proportioning Methodology for Structural Sand-Lightweight Concrete

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